DOPAMINE RELEASE DURING COCAINE SELF-ADMINISTRATION IN RATS - EFFECT OF SCH23390

This experiment tested the hypotheses that: (1) self-administration of cocaine would produce an increase in dopamine (DA) oxidation current in the nucleus accumbens (n. ace.); and (2) a faster rate of cocaine i ntake in the presence of a D-1 receptor antagonist would produce a gre ater increase in DA levels. Rats trained to self-administer cocaine un der a fixed-ratio 2 schedule were implanted with stearate-modified gra phite paste electrodes bilaterally in the n. ace. The effect of pretre atment with the D-1 receptor antagonist, SCH23390, on the DA oxidation current associated with self-administration of cocaine (1 mg/inj.) or saline was investigated using chronoamperometry. Pretreatment with SC H23390 produced a 2-fold increase in the amount of cocaine intake. Thi s in turn resulted in a 2-fold increase in the DA oxidation current re corded in the n. ace. Pretreatment with SCH23390 did not, however, pro duce any significant change in either the number of saline injections received or the DA oxidation current recorded during saline self-admin istration. These findings show that cocaine increases DA oxidation cur rents in the n. ace., and that both the rate of cocaine self-administr ation and the magnitude of these currents increase even further follow ing SCH23390. The results also imply that the baseline rate of cocaine self-administration does not result in the occupation of all possible DA transporter sites.